Summary Osteoarthritis (OA) is a painful and debilitating disease of the synovial joints, affecting over 27 million people in the United States. The prevalence of obesity has risen dramatically in the past two decades, and we now know that obesity is likely to be the primary preventable risk factor for OA. The goal of this project is to examine the influence of dietary fatty acids in obesity-associated OA in mice, and to examine their interaction with altered biomechanical and pro-inflammatory factors using various in vivo and in vitro models. We propose that low-grade chronic systemic inflammation ? due to obesity or pro-inflammatory fatty acids in the diet ? acts in synergy with local inflammatory cytokines or altered mechanical loading following injury to promote a state of inflammation and matrix degradation in the articular cartilage. In Aim 1, we will examine the role of a high-fat diet rich in omega-6 fatty acids in the development of OA, and we will examine the effects of endogenous conversion of omega-6 to omega-3 fatty acids to mitigate OA severity in the Fat-1 transgenic mouse. In Aim 2, we will examine the effects of systemic or local gene therapy using the Fat-1 gene to mitigate obesity-induced OA. In Aim 3, we will use controlled in vitro models of cartilage explant loading to examine the effects of mechanical stress in combination with pro- inflammatory cytokines and fatty acids on the anabolic and catabolic activities of the chondrocytes. Detailed studies of the interactions between specific dietary composition, pro-inflammatory mediators, and tissue metabolism in articular cartilage will improve our understanding of the pathology of the OA, particularly as it relates in vivo to biomechanical factors such as obesity or injury. The results of this study will provide new insights into key elements of the pathogenesis of obesity-induced, and ultimately could lead to new treatments that exploit dietary or gene therapies to prevent disease. ! !